I read this in under two hours and it wasn't bad or anything just not very memorable. I don't think I'll remember the plot in a year or even a few months.
Marie Lu is a good wrriter, I enjoyed her series but couldn't even finish Warcross-- it bored me. With Batman its just another YA about a teen who lost his parents meets a girl and falls in love with her. Just add Batman to the mix and its a DC series.
So fun, and a quick read but nothing special.